A process has been developed for the removal of ions from solution. The process incorporates an electrolytic cell in which particulate material is spaced between two electrodes. A bed of particulates acts as a bipolar electrode which removes or destroys ions as the solution flows through the bed. The unique feature of the process is the composition of the bed which comprises a mixture of both electrically conductive and non-conductive material. The scheme provides for the efficient removal of the ions.
Andrus in U.S. Pat. No. 4,004,994 discloses a process for the electrochemical removal of contaminants from solutions. This process makes use of an electrolytic cell which comprises a bipolar bed of conductive particles. As a current is passed through the cell, ions are attracted to the bipolar electrode and are either destroyed or plated out. Usually such a process is designed to treat waste streams from plating operations and other metal finishing processes. Typically these waste streams contain low concentrations of salts which present environmental hazards.
Although the use of such bipolar processes shows much promise, they are handicapped by operational difficulties. Generally the concentrations of ions in the waste streams are low, and thus the electrical resistance of such liquids is high. On the other hand, the electrical resistance of the bipolar bed is relatively low. The result of this mismatch is that a large portion of the electrical current is shunted or short-circuited through the bipolar bed without producing an electrochemical effect.
Several steps have been proposed to improve the efficiency of bipolar beds. Andrus focuses attention on the contact resistance between the particles in the bipolar bed. This contact resistance can be modified within limits by controlling the compaction of the particles, the shape and sizes of the particles, and the flow rate of the solution through the bed.
An alternative approach has been proposed by Salter et al. in U.S. Pat. No. 3,716,459. This process depends on the application of a restricted fluidized bed in which the bipolar particles undergo movement and the bed is allowed to expand to a limited extent. In such a fashion the electrical contact between particles can be controlled.
More recently, U.S. Pat. No. 6,010,604 disclosed a neural network packing for use in the scrubbing of gages by an aqueous liquid. The packing comprises pieces of material that are electrically conductive and pieces of another material that are non-conductive. These pieces are randomly intermixed and spaced between two electrical contacts. This packing, while showing considerable promise, is restricted to the use of scrubbing gases.
Therefore, it is an object of the present invention to utilize the best features of the prior art to achieve a process designed to treat solutions by passing such solutions through an electrolytic cell to remove or otherwise alter dissolved ions.
Furthermore, it is an object to provide for a process that is efficient in operation and easy to use.
These and other objects, features and advantages of the invention will be apparent from the accompanying drawing and the following description.